Here is a set of digital sketches from December 2010 thru Early February 2011 done in Sketchbook Pro for the iPad.
There is a mixture of Star Wars, Star Trek (I.S.S. Voyager and other Starships) and my own creations. There is also a scene from my Action Force Pages that I imported into the app and did a quick color to my lines.

Is the Titan Supposed to be a Heavy Battle cruiser something more powerful then say a Sovereign Class? Also I thought I was clever making up some specs for my own Spartan Class ship , however i am Less artistically inclined than you, so my version is a tad different and only in word format as of yet. But The Spartan Idea is probably similar, less head room decks closer together, more room for weapons and fuel less for personnel. I was on a Submarine so I figure Star fleet personnel could handle not having huge personal quarters or windows in every room.

The I.S.S Titan is a Light Battle Cruiser the Sovereign is more powerful in my opinion. What makes her more powerful than the U.S.S. Titan is that she has more offensive weapons and has a multivector mode. She is also faster than her Federation counterpart at sublight speeds with the addition of the Battle sections Impulse deck.

I honestly kinda like the Sovereign class-like ship towards the bottom out of the three as an Enterprise-F concept. That is definitely because I see all subsequent Enterprises as sleek vessels, and less stocky or utilitarian, as is seen with the Congo class (Enterprise-G) and Universe-class (Enterprise-J), even with their oval shaped saucers.
I personally think that I would have found your design for the Enterprise-F more acceptable if you had found a way to combine the boomerang-shaped primary hull with a sleeker engineering hull.
Knowing me, I'll probably devote more than a few sketches experimenting with the boomerang-shaped primary hull. I have already found that it can make a nice shape for the primary hull of a vessel of the Sabre-type configuration.
The concept on the right has a nice shape for the primary hull. I would personally move the nacelles and pylons closer to the aft of the ship, but that is just me. The primary hull has a cool, aggressive shape, which to me looks makes me think that this design could be good for a vessel meant for tactical situations/combat. I personally think this could be a good shape to recycle for a later design if you ever get the chance.

The I.S.S Titan is a Light Battle Cruiser the Sovereign is more powerful in my opinion. What makes her more powerful than the U.S.S. Titan is that she has more offensive weapons and has a multivector mode. She is also faster than her Federation counterpart at sublight speeds with the addition of the Battle sections Impulse deck.

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I always thought that the Federation Titan should also have hull separation capabilities. I would think that Starfleet would give many of their finest vessels this ability, especially after giving the Sovereign class this ability, and after much of the crew of the Enterprise-D were saved thanks to this feature. Is it okay to assume that the U.S.S. Titan and her sisters eventually received a refit that allowed them to have hull separation capabilities similar to the I.S.S. Titan?

Recently as a test image for a possible ongoing freelance gig I had to create a test
hockey jersey and submit it. While this is not the image from that test I figured I would have
some fun with the template I used. So here are two samples of themed Hockey Jersey Designs.

Looks appropriate for DS9/FC era, although I'm not too sure about the yellow band on the sleeves. I know the shade of red used for the uniforms and the markings are different, but when they're brought together like this something seems off, especially with the collar. Not sure if it would look any better if you picked one shade or maybe compromised between them. Oddly enough, the two different shades of red look good on the Blood Barons jersey.

Ever think about adding some realistic textures to it like this or this?

Recently as a test image for a possible ongoing freelance gig I had to create a test
hockey jersey and submit it. While this is not the image from that test I figured I would have
some fun with the template I used. So here are two samples of themed Hockey Jersey Designs.

Over the years doing my Dark Mirror Universe Characters and Ships I have been constantly asked if I was going to ever do any thing with the character while Posted on the I.S.S. Enterprise. Well here is you answer...Yes

I am about to start another sample set of pages to send to IDW and I have a sample script for Star Trek The Next Generation Intelligence Gathering. I am going to go by that script and instead of having it in the TNG universe I am going to do it in the Dark Mirror Universe. So here is my first character sketch of Cmdr Riker how I see him looking.